Retroactive Skill Points (3.5e Variant Rule)

From D&D Wiki

Whenever your intelligence modifier increases permanently (through levels, wishes, templates, class features, etc.), you gain skill points retroactively. You must use these skill points as if you had that intelligence score since you began adventuring.

Example: A ranger 5/monk 2 with a 13 intelligence gains an extra point of intelligence when he gains another level in monk. This gives him 8 extra skill points to spend on ranger skills (with a max rank of 8 before they are considered cross-class) and 3 extra skill points to spend on monk skills.